An evaluation of RAPD markers in a cladistic analysis of pea
Random amplification of polymorphic DNA (RAPD) is a new DNA polymorphism assay that uses the polymerase chain reaction (PCR) to amplify random DNA segments from single primers of arbitrary nucleotide sequence. These amplified segments can be used as "fingerprints" to characterize plant types by comparing their polymorphisms. I use RAPDs, in conjunction with allozyme markers and classical morphological traits, to characterize the genus Pisum biosystematically. The genus is often divided into three wild species, Pisum fulvum, P. humile and P. elatius, as well as the cultivated P. sativum-, each has been studied for morphological, karyomorphological and genetic traits. The focus of this study was to apply RAPD markers, allozymes and morphological data to evaluate relationships within and among wild and cultivated pea accessions. Comparisons among markers were of value as well in assessing their relative usefulness for evolutionary studies. The data reveal that morphological characters do arrange the pea taxa in large measure according to traditional groupings. Allozymes, by comparison, do not provide substantial resolving power, either alone or when combined with either morphological or RAPD characters. RAPD characters clearly provide more resolving power than the allozymes and begin to approach the informativeness of the morphological characters as their numbers are increased. Overall, a mixture of character types appears to provide the cladogram closest to expectations. These findings generally corroborate past hypotheses respecting the relationships among taxa within the genus Pisum. P. fulvum populations are shown to be distinct outliers clearly different from P. humile, P. elatius and P. sativum, while the southern P. humile form a strong monophyletic group. Northern P. humile, P. elatius and P. sativum appear to comprise a species aggregate, with P. elatius most closely related to P. sativum-, However, northern P. humile may be the progenitor of both.